This invention relates to a method for preparing a homogeneous aqueous composition comprising a polydimethylsiloxane and a durable press resin and to the compositions obtained therefrom. By durable press it is meant herein the wrinkle-resistant property and/or the permanent-crease property displayed by resin-treated cellulose-containing fabrics.
Durable press resins and silicone compositions have been individually used for a long time to provide improved properties of textiles. In addition, to further improve the physical properties of textiles treated with durable press resins, silicone materials have been combined with durable press resins to provide improved hand, tear strength, and abrasion resistance to the treated textile.
It is known, for example, to prepare a textile-treating bath by admixing an aqueous emulsion of a hydroxy-endblocked polydimethylsiloxane with an aqueous solution of a durable press resin in the presence of additional water and optionally, a surfactant. Furthermore, it has been disclosed and claimed by Rooks in a copending U.S. patent application, Ser. No. 895,827, filed on Apr. 13, 1978 and assigned to the assignee of this application, that a textile-treating bath may be prepared more advantageously by blending the concentrated aqueous emulsion of a hydroxy-endblocked polydimethylsiloxane with the concentrated aqueous solution of a durable press resin and, optionally, a surfactant, thereby obtaining certain processing advantages, and thereafter diluting the blend with additional water. The blends of Rooks are particularly stable to the skinning-over that often occurs with silicone emulsions that are exposed to the atmosphere.
One disadvantage of the above methods is the tendency of the silicone emulsion and the blend of silicone emulsion with durable press resin solution to separate, such as by creaming or occasionally by breaking, after being subjected to one or more freeze-thaw cycles. Although the blends are easily reemulsified, problems with storage of these materials are introduced by this disadvantage.
Another disadvantage of the above methods is the necessity of processing, shipping and storing relatively large quantities of water as a component of the silicone emulsion, the durable press resin solution and their blends that are used to prepare the textile-treating bath. Additional economies could be realized if the quantity of water in these compositions that are subsequently used to prepare the textile-treating bath could be reduced.
The present method comprising emulsion polymerization of lower-molecular-weight polydimethylsiloxanes in a solution of durable press resin provides a means for overcoming the above-mentioned disadvantages. The resulting homogeneous aqueous composition obtained therefrom has improved stability to separation after freeze-thaw cycling. In addition, since the water of the homogeneous aqueous composition of this invention serves a dual role in dissolving the durable press resin and functioning as the continuous phase during the emulsion polymerization of the polydimethylsiloxane, more highly concentrated compositions are made available, greater economies are realized and compositions of greater utility are obtained than are present in the prior art.
Polymerization of siloxanes in aqueous emulsion is well known from Hyde et al., U.S. Pat. No. 2,891,920; Findlay et al., U.S. Pat. No. 3,294,725; and Axon, U.S. Pat. No. 3,360,491. Further improvements are disclosed by Ikoma, U.S. Pat. No. 3,697,469 and by Huebner et al., U.S. Pat. No. 3,706,695. In addition, British Pat. No. 1,161,072 describes the polymerization of polysiloxanes in an aqueous emulsion comprising an olefinically unsaturated organic monomer. However, none of these references indicate that emulsion polymerization of siloxanes can be accomplished in an aqueous solution of a durable press resin. It was unexpected to find that polydimethylsiloxanes could be emulsion-polymerized in an aqueous solution of a durable press resin using a strong acid catalyst since it is known that durable press resins are normally cured with an acid catalyst or latent acid catalyst. It was also unexpected to find that the resulting composition comprising a polydimethylsiloxane and a durable press resin had improved stability toward separation after freeze-thaw cycling, compared to a blend of polydimethylsiloxane emulsion and durable press resin solution.